1. Field of the Invention
The present invention concerns a rotary cutting head using wire-shaped flexible cutting elements. It is advantageously intended for equipping portable cutting devices such as grass cutters, edge cutters, motorized brush cutters or mowers, hedge cutters and similar.
More precisely, the invention concerns a rotary cutting head using strands of flexible cutting wire constituted by lengths of wire, rods or slender sticks, made of any suitable material such as ‘Nylon’® or other appropriate flexible material.
The invention concerns also portable cutting devices equipped with the cutting head disclosed in the description below.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
Motorized tools equipped with such cutting heads are currently used by professionals as well as private individuals. By way of examples documents US-2001/0023542, U.S. Pat. No. 6,401,344, U.S. Pat. No. 6,944,956, WO-2004/064489, WO-2005/032237, WO-2006/017372, WO-2008/139246, FR-2888085 are cited which describe various possible fittings of cutting heads using cutting elements constituted by strands of flexible cutting wires.
These cutting heads are mounted at the distal end of a handle equipped with a U-shaped handle or dual guide and control handle for the rotational drive motor of said cutting heads, and with a ring for attaching a carrying harness.
A cutting head of this kind supports one or several (most often two) wire-shaped cutting elements extending radially towards the outside, each cutting element presenting a predetermined limited length. The body of the cutting head features, laterally, at least one inlet opening for the engagement of a strand of cutting wire, and, in certain embodiments, at least one opposite opening for the removal of used or damaged cutting wire(s).
A clamping mechanism is housed in the body of the cutting head, this mechanism enabling, on the one hand, the driving in of one of the end portions of the cutting strands into the rotary cutting head, and, other hand, opposing the inverse movement of said strands which are thus locked in an active assembly position. This mechanism includes, most often, a toothed toggling cam subjected to the action of a pressure device.
According to document WO-2006/017372, each strand of cutting wire presents a predetermined length and can be squeezed, in a detachable manner, in an essentially closed chamber, by means of a squeezing mechanism including a mobile clamping element and a spring which tends to push said clamping element against the proximal end of the strand of cutting wire engaged in said chamber. A releasing element (special tool or screwdriver) is necessary to cooperate with the clamping element in order to move the latter away from the strand of cutting wire, to meet the antagonistic action exerted by the spring, in order to withdraw said strand of cutting wire from the cutting head.
In this case, to perform the replacement of a strand or the two cutting strands that are used or damaged, appropriate tools need to be available in order to proceed successively to the neutralization of the springs maintaining said strands in position. Besides being a constraining intervention which requires a certain knowledge and familiarity with the tool, this arrangement does not permit to modify the active length of the cutting strands while the device is being used, without going through the inconvenience pointed out above. Furthermore, the cutting strands cannot traverse the cutting head, because the axis or drive shaft providing the rotation of said cutting head passes through the middle of it. The operators are therefore obliged to use relatively short cutting strands, which increases the frequence of their replacement owing to wear.
Document US-2001/0023542 describes a cutting head provided with four side openings to allow the engagement and removal of four cutting strands. The proximal part of each of these strands is engaged in a closed chamber kept in position of active implantation by a dedicated clamping device for each strand. The control element of each clamping device is constituted by a sliding bar which is accessible from the upper face of the housing of the cutting head. Each clamping device is constituted by two horizontal cams subjected to the action of springs between which a strand of cutting wire can be engaged and squeezed. The clamping cams are punctually opened by activation of the sliding control bars placed on the upper part of the cutting head for the purpose of freeing the worn strand and or to allow insertion of a new strand. During the release of the sliding bars, the clamping cams come closer together to exert a squeezing action on the strand under the action of the spring.
Utilization of the cutting head described in this document leads to the same inconveniences as those pointed out previously concerning document WO-2006/017372, with, additionally, the inconvenience of a more complex fitting and utilization.
The length of the cutting strands is reduced, requiring consequently more frequent replacements of the worn strands. Two cams are necessary to block each cutting wire which increases the number of components and complicates the manufacture of the devices.
To remove the used wire, it is necessary:                either to extract the wire from below and through the center of the head by simple traction, after having removed the sliding bowl;        but one must have beforehand let a length of wire protrude, because otherwise this is impossible;        the area where to seize the wire strand for the purpose of extracting it is subject to clogging;        or actuate the control bar to unlock the cams;        unlocking is done wire by wire and each control bar must be actuated independently which causes a loss of time;        the control bars are of small dimensions and therefore difficult to manipulate while wearing gloves;        moving the control bars relative to the exterior bell of the cutting head requires some play and thus a risk of clogging and binding.        
Document U.S. Pat. No. 6,401,344 describes a cutting head of a brush cutter.
This cutting device uses a traversing single strand wire and as such generates a significant loss of wire (the entire center of the head). If the wire breaks on one side of the head, it is obligatory to replace all of it. The unlocking bars are located at the outside, and hence subject to clogging.
The locking mechanism, in active position, of the single strand of cutting wire in the cutting head is constituted by a complex system of squeezing range which does not allow an automatic locking of the cutting wire, in this position.
The devices described in the documents above, and generally speaking, all cutting heads of the state of the art using flexible cutting strands, have these disadvantages:                the difficulty, or even in certain cases, the impossibility of making adjustments to the length of the cutting strands depending on the work to be done;        the time needed for removing worn cutting strands and for their replacement, because it is obligatory to wear gloves which complicates the manipulations;        clogging of exterior control devices for unlocking the blocking means of the cutting strands;        the need for having available a tool for opening the cutting head and unlocking the worn or damaged cutting strands.        